The setup of a PC for Remote Assistance becomes alsmost as important as a good backup policy. Although granting access to your system may create security threats, temporary connections can be made without too many compromises.
VNC is a good Freeware software that helps you around on different OS platforms. In most cases only Component One will suffice to get the job done:
Check here if your VNC Server is running and can be accessed from the Internet.
If you have any questions, check VNC FAQ-o-Matic
Check also my post on port forwarding with VNC.
Component Two: Install No-IP (optional)
For easy retrieval over the Internet, assign a DNS name to your PC. No-IP offers a free dynamic DNS support.
Component Three: Install Putty (optional)
If you are concerned about the security, you may get TightVNC and Putty to work